Among different nanostructures, one-dimensional structures having a large aspect ratio are called nanowires or nanorods, and synthesis thereof using various materials has been developed significantly. Particular examples of such nanostructures include carbon nanotubes (CNT), cobalt silicide (CoSi), etc. Particularly, it is known that nanostructures grown in the form of nanorods have the advantages of higher crystallinity and lower potential density as compared to those grown in the form of thin films. Carbon nanotube powder has already been developed commercially as a transparent electrode or a negative electrode part for electric field emission.
However, such nanorods are not sufficient to be used in any functional device other than a transparent electrode, because they have an excessively small size and low strength. There has been an attempt to develop a field emission transistor (FET) or the like by forming a junction between an individual semiconductor nanorod and a metal, followed by heat treatment. In addition, there has been developed a process including growing semiconductor nanorods on a heterogeneous wafer (a wafer different from a semiconductor material to be grown in terms of a structural form or chemical composition) (e.g.: growing a GaN single crystal thin film on a single crystal sapphire wafer or growing a CuInSe2 thin film on amorphous glass), filling a gap between semiconductor nanorods with an amorphous matrix material, such as silicon dioxide or polyimide, and planarizing the top thereof to form a junction with a metal. However, such a process is still problematic in that the resultant nanorods have low length uniformity and are limited in light emitting surfaces. It is required for a device containing nanorods to be linked amicably with a follow-up process, such as forming an electrode.
Zinc oxide (ZnO) is a material having a wurtzite structure with a hexagonal crystal system, and is a direct transition semiconductor having high transmission of visible light, a relatively high refractive index and dielectric constant and a broad band gap of 3.37 eV. Particularly, since the free exiton bonding energy of zinc oxide is up to 60 meV at room temperature, it is expected that zinc oxide has a higher light extraction ratio caused by optical excitation as compared to currently used gallium nitride. Thus, many studies have been conducted about zinc oxide. Moreover, when zinc oxide nanorods per se function as a cavity for laser generation, laser generation at room temperature may be expected in such nanorods.
However, various methods have been used to prepare zinc oxide but use of zinc oxide has been limited because of difficulties in p-doping. Although some laboratories have provided reports of p-doping results, there are many rooms for improvement in terms of efficiency and reliability.
There has not been reported about laser generation caused by p-n junction of zinc oxide nanorods. Laser generation caused by optical pumping instead of excitation caused by electrical pumping is merely known.